Trans-fats may negatively affect sperm levels: Harvard study

Trans fats in human cells can act as a biomarker of diet, say Harvard scientists

Increased intakes of trans fats may reduce a man’s sperm concentration, a measure of fertility, according to new findings from Harvard School of Public Health.

The data, which was obtained from only 33 men, adds to an ever increasing body of science supporting the detrimental effects of trans fats, previously linked to increased risks of cardiovascular disease.

“We found that trans–fatty acids were present in human sperm and were related inversely to sperm concentration,” wrote researchers, led by Jorge Chavarro, MD, ScD, in the journal Fertility and Sterility.

“Our data are in agreement with experimental data in rodents showing that trans–fatty acids can affect spermatogenesis profoundly,” they added.

Dr Chavarro and his co-workers cautioned, however, that their study has limitations, and givem the “potential clinical and public health implications of our findings, it is important that these hypothesis generating findings be re-evaluated in larger, better-designed studies and that the relation between intake of trans–fats and sperm levels of these fatty acids be examined closely”.

Trans fats and heart health

Though trace amounts of trans fats are found naturally, in dairy and meats, the vast majority are formed during the partial hydrogenation of vegetable oil (PHVO) that converts the oil into semi-solids for a variety of food applications.

Trans fats are attractive for the food industry due to their extended shelf life and flavour stability, and have displaced natural solid fats and liquid oils in many areas of food processing.

But scientific reports that trans fatty acids raise serum levels of LDL-cholesterol, reduce levels of HDL-cholesterol, can promote inflammation can cause endothelial dysfunction, and influence other risk factors for cardiovascular diseases (CVD), has led to a well-publicized bans in places like New York City.

Denmark introduced legislation in 2004 that required locally and imported foods to contain less than two per cent industrially made TFAs, a move that effectively abolished the use of partially hydrogenated vegetable oils in the country.

In the food industry this has been mirrored by an increase the in pressure on food manufacturers to reduce or remove trans fatty acids from their products and reformulate.

Study details

The new study involved the analysis of 33 semen samples collected as part of a pilot study. The fatty acid composition of the sperm showed that higher levels of total polyunsaturated fatty acids and the omega-3 docosahexaenoic acid were related to improved sperm concentrations.

On the other hand, sperm with the highest levels of trans-fatty acids were found to linked to lower sperm concentrations.

“To our knowledge, this is the first study demonstrating the presence of trans–fatty acids in human sperm and a relation between sperm trans–fatty acids and sperm concentration in humans,” wrote the researchers.

“Because human fatty acid metabolism cannot introduce trans double bonds into a fatty acid chain, the presence of trans–fatty acids in a human cell or tissue implies dietary intake and can serve as a biomarker of diet.

“Our results suggest that higher intake of trans–fatty acids is related to a lower sperm concentration. However, it is not possible to know from our data what dietary intake levels are necessary to achieve the sperm trans–fat levels associated with reduced sperm concentration nor the timing between intake and any eventual effects on spermatogenesis,” they added.